1. Field of the Invention
The present invention relates to a holding cabinet, which provides a more consistent and accurate holding environment for food products. In particular, the invention relates to a holding cabinet, which provides a more consistent and accurate holding environment for food products by providing closed-loop control of the humidity within the cabinet as a controlled process variable.
2. Description of Related Art
With the increasing popularity of xe2x80x9cfast foodxe2x80x9d establishments where food is precooked for later sale, there is a demand for food holding devices that maintain food at a substantially uniform temperature for selected periods of time while preserving the taste, moisture content, texture and quality of the food. Further, in other applications, it is desirable to be able to restore food, particularly baked goods, to acceptable quality after long storage periods.
In many instances, storage of xe2x80x9cfast foodsxe2x80x9d is particularly difficult because heat loss, bacteria growth and moisture loss experience by the food at storage conditions provided by prior art devices, particularly where the food is to be stored warm, contribute to rapid deterioration of the food.
More particularly, it has been found that air circulation characteristics and improper storage temperature contribute significantly to bacteria growth and excessive loss of moisture which leads to food shrinkage, so that in improper storage atmosphere the food deteriorates after only a short period of time and loses its tenderness, appetizing taste, and appearance.
It has also been found that even where food is stored under favorable conditions in an enclosure, the food deteriorates at a rate dependent on the time the door to the enclosure is opened so the storage chamber is exposed to the ambient atmosphere.
Additionally, it is known that in storage of some foods, such as fried chicken or fish, where a crust is provided, it is particularly desirable to maintain the crispness of the crust while minimizing the moisture loss from the underlying meat. Storage of such foods tends to involve the satisfaction of seemingly mutually exclusive conditions, to hold the crispness of the crust by maintaining low moisture content in the crust while minimizing moisture loss from the food. In such foods, excessive moisture-loss results in shrinkage and loss of tenderness and adversely affects the texture of the meat. This may be prevented by controlling the temperature and humidity of the storage atmosphere. The problem is to prevent moisture flow from the underlying food to the crust while holding the crust in low moisture content.
There are presently numerous cabinets for holding food products or other items in a temperature and humidity-controlled state. These cabinets, however, suffer from a common shortcoming. When the cabinets are opened to insert additional food products or other items or to remove such products or items from the cabinets, heat and humidity are lost. Unless the lost heat and humidity is restored, the items stored in the cabinets may cool or dry out, or both.
Proofing and holding are distinct food preparation processes. Proofing is a process generally applied to yeast bread products, in which the yeast grows and the bread rises due to yeast growth by products. Holding, however, is a process during which food characteristics are maintained, e.g., the temperature, moisture content, texture, and color of the food remain unchanged. Thus, in proofing, food product characteristics change, while in holding, those characteristics remain the same.
In terms of process parameters, proofing may be distinguished from holding mainly by lower process temperatures. Humidity may be greater than about 80% RH, but the selected humidity may vary widely depending on the particular bread product to be proofed. Nevertheless, proofing temperatures are generally lower than holding temperatures. High proofing temperatures might inhibit yeast growth. However, high holding temperatures are desirable because such temperatures may suppress the growth of bacteria, molds, and the like and may increase the holding time for food products.
Previously, various methods and devices have been developed to attempt to maintain heat and humidity. For example, pans of water have been placed in the cabinets and allowed to evaporate naturally in an attempt to maintain humidity. Despite its simplicity, this method has not been completely successful. Natural evaporation does not quickly compensate for humidity losses. Further, while humidity naturally increases, items stored in the cabinets are subject to the drying effect of heat. Moreover, because natural evaporation is effected by the temperature within the cabinet, the rate of humidity adjustment may fluctuate with temperature changes, but humidity adjustments will probably lag behind such temperature changes.
Systems have been developed by which the heat and humidity levels of air within a cabinet are more closely controlled. Air may be heated by passing it over, across, or through various types of heating elements. Air may also be passed over, across, or through water in order to raise the humidity of the air. Despite these improvements, known systems remain unable to precisely adjust for losses of heat or humidity due to disruptions to the cabinet environment, such as opening and closing the cabinet access, and adding or removing food products or other items.
Further, the addition of heating elements and humidity generating means create additional problems. If heat or humidity rise too quickly, the air within the cabinets could become overheated or too moist. Such uncontrolled fluctuations in heat and humidity may be detrimental to food product or other items stored within the cabinets.
Cabinets commonly are equipped with thermostats in an attempt to control the heat of the air circulating within the cabinets. By controlling the air temperature, however, the humidity of the air also may be affected. Nevertheless, such controls alone do not provide adequate control of the humidity within the cabinet. Moreover, a thermostat or manual potentiometer may not maintain temperature and humidity within predetermined parameters. Generally, such devices only cause the heating elements to heat the air when the air temperature falls below a set value.
A need has arisen for a holding cabinets for attaining closed-loop humidity control by means of an effective humidity transducer. Still a further need has arisen for a cabinet that may be used for both proofing and holding. It is a feature of such a cabinet that its control system defaults to a generally higher temperature associated with a holding mode of operation. It is an advantage of this default setting that the cabinet may inhibit the growth of bacteria in food products.
A holding cabinet with closed loop humidity control system and method for controlling humidity in a holding cabinet are disclosed. According to an embodiment, the method comprises determining a relative humidity set point; activating a heater in a fluid pan; determining if a fluid is present in the fluid pan; measuring the relative humidity in the cabinet; and maintaining the relative humidity within a predetermined range. According to another embodiment, a holding cabinet with a closed loop humidity control system includes a holding cabinet; an air temperature probe for measuring an air temperature within the holding cabinet; a humidity sensor for measuring a humidity within the holding cabinet; a heater for heating air within the holding cabinet to a predetermined temperature; a fan for circulating the air and for introducing air from outside the holding cabinet; a slide vent and motor; and a water pan for holding water within the holding cabinet.
According to another embodiment of the present invention, a system for humidity measurement includes a humidity sensor; an oscillator circuit; and a microprocessor to measure oscillator frequency. According to another embodiment of the present invention, a system for maintaining a relative humidity level in a cabinet includes means for determining a relative humidity set point; means for activating a heater in a fluid pan; means for determining if a fluid is present in the fluid pan; means for measuring the relative humidity in said cabinet; and means for maintaining the relative humidity within a predetermined range.
Other objects, features, and advantages will be understood by persons skilled in the art from the following detailed description of preferred embodiments of the present invention, in view of the accompanying figures.